Solutions in which a chemical is dissolved in water are commonly referred to as aqueous solutions. Some aqueous solutions conduct electricity; this property is referred to as conductivity. The conductivity of an aqueous solution depends on the solution's concentration, which is a ratio between the amounts of chemical and water in the solution, and the solution's temperature.
The conductivities of some concentrations of some species (i.e., chemical types) of aqueous solutions are well known. For example, the conductivities of many different concentrations of sulfuric acid have been measured at several temperatures by Darling and other researchers. These conductivities are often presented in the form of reference conductivity curves. A reference conductivity curve shows the relationship between conductivity and concentration for a species of aqueous solution at a reference temperature. FIG. 6 shows reference conductivity curves for sulfuric acid at reference temperatures of 0° C., 18° C., or 25° C.
Since the conductivity of an aqueous solution depends on its concentration, a measurement of conductivity is often used to deduce concentration. This measurement is compensated for temperature by scaling it to the conductivity that the solution would have if the temperature of the solution were brought to the reference temperature of a reference conductivity curve for the species (e.g., 0° C., 18° C., or 25° C. for the curves for sulfuric acid shown in FIG. 6). This scaling depends solely on temperature and results in a compensated conductivity. The compensated conductivity is then compared to the reference conductivity curve, and the concentration of the solution is determined to be the reference concentration whose reference conductivity most closely approaches the compensated conductivity.
The ratio between absolute conductivity and compensated conductivity is usually referred to as the temperature compensation factor. The temperature compensation factor for most species of aqueous solutions depends relatively strongly on temperature and relatively weakly on concentration. As such, computing the temperature compensation factor based solely on temperature, but not on concentration, is sufficient for ordinary applications, e.g., applications that do not require high degrees of accuracy. (In other words, assuming that different concentrations of a solution have the same temperature compensation factor is usually a sufficient approximation for ordinary applications.) Computing the temperature compensation factor based solely on temperature is not sufficient, though, for applications that require high degrees of accuracy.
Unfortunately, while a solution's temperature can be measured prior to compensating the solution's conductivity, the solution's concentration cannot be determined until after compensation. Present scenarios for determining compensated conductivities, compensation factors, concentrations, and other related solution parameters have, therefore, limited accuracy.